1. Field of the Invention
The present invention relates to a mobile communication system, a radio terminal used therefor, a radio network controller and an operation control method therefor. In particular, the present invention relates to a mobile communication system, which has a function for broadcasting or multicasting service data including large volume contents such as voices and images to a plurality of radio terminals (users), and a radio terminal used therefor, as well as a radio network controller and an operation control method therefor.
2. Description of the Prior Art
In a mobile communication system, there is a service for broadcasting or multicasting large volume data of program contents to a plurality of radio terminals. This service is called an MBMS (Multimedia Broadcast Multicast Service). A schematic block diagram for such an MBMS function is shown in FIG. 5. Referring to FIG. 5, a BMSC (Broadcast Multicast Service Center) 1 is connected to an IP (internet Protocol) network 30 and is also connected to a plurality of RNCs (Radio Network Controllers) 4 and 5 via a GGSN (Gateway GPRS (General Packet Service) Support Node) 2 and an SGSN (Serving GPRS Support Node) 3.
The RNC 4 has NodeBs (radio base stations) 6 and 7 under its control and the RNC 5 has a NodeB 8 under its control. The respective NodeBs 6 to 8 are adapted to cover one or more cells 9 to 11, which are service areas. In the figure, for simplification of explanation, each NodeB is shown to cover one cell. Reference numeral 20 denotes a UE (user equipment), which indicates a radio terminal.
Note that interfaces between the SGSN 3 and the RNCs 4 and 5 are referred to as Iu, and interfaces between the RNCs 4 and 5 and the NodeBs 6 to 8 are referred to as Iub. Moreover, Iur also exists as an interface between the RNCs 4 and 5.
In the case in which the UE 20 shown in FIG. 5 desires delivery (broadcast/multicast) of the above-described MBMS service data, procedures shown in FIG. 6 are executed between the UE 20 and the BMSC 1. In other words, “SUBSCRIPTION” for application for subscribership in the service is generated by the UE 20 and sent to the BMSC 1 through the RNC 4 (step S1). Then, “SERVICE ANNOUNCEMENT” for announcement of the service is sent from the BMSC 1 (step S2), and “JOINING” for requesting to join the service is sent from the UE 20 in response to “SERVICE ANNOUNCEMENT” (step S3). Then, “MBMS MULTICAST MODE BEARER SET UP”, which is bearer setup for the MBMS, is applied to the RNC 4 by the BMSC 1 (step S4).
Then, “MBMS NOTIFICATION” for notifying of the MBMS is sent from the RNC 4 to the UE 20 (step S5), and data of the MBMS is sent from the BMSC 1 to the RNC 4 (step S6). Thereafter, the data is delivered to the UE 20 (step S7). When delivery of all data ends, “MBMS MULTICAST MODE BEARER RELEASE” for bearer release is sent from the BMSC 1 (step S8), and “LEAVING” indicating withdrawal from the service is sent from the UE 20 (step S9) to end the processing.
Such a procedure shown in FIG. 6 is only an outline. Details of the procedure are disclosed in the recommendation of the 3GPP (THIRD GENERATION PARTNERSHIP PROJECT).
In such an MBMS, the RNC transfers service data to each UE in the cell under its control by the PtP (Point to Point) system or the PtM (Point to Multipoint) system. It is decided according to the number of UEs, which are existing in the cell and joining to be planned to receive the service data, whether the PtP system or the PtM system is used (see the above-described document). In other words, when the number of UEs has reached a fixed value (threshold value) or more, in terms of saving transmission power, the RNC delivers the service data by the PtM system. Conversely, when the number of UEs has fallen below the threshold value, the RNC delivers the service data by the PtP system.
After the UE has joined the service of the MBMS (step S3 of FIG. 6), there is a short time until the UE actually becomes capable of receiving the service data (step S7). During the time, movement of the UE between RNCs may occur. In other words, in FIG. 5, it is possible that the UE 20 joins the service of the MBMS while it is in a zone of the cell 10 of the NodeB 7 under the control of the RNC 4, and before receiving the service data, moves to the cell 11 of the NodeB 8 under the control of the RNC 5.
In such a case, the UE 20 notifies a moving destination RNC 5 that it has moved to the cell 11 under the control of the moving destination RNC 5. Thus, the moving destination RNC 5 is capable of learning that the UE 20 has moved thereto. However, in the current system, the moving source RNC 4 has no means for learning that the UE 20 has left the cell 10 under its control.
As described above, in the RNC, in delivering the service data of the MBMS, it is decided according to the number of UEs, which are planned to receive the service data, whether the PtP system or the PtM system is used. Thus, the RNC is required to grasp the number of UEs. However, the moving source RNC cannot learn the number of UEs.